Ready for wierd answer number 500?
First go to the husqvarna web site. And down load this owners manual.
Yes, I know it is written in swedish... (Not a Joke)..
Go to page 59 and page 60 and find YOUR particular mower deck.
It could be 42, 36, or 32 inches.
Make sure the pully system and bracket system is the same as on your deck.
Zoom into 300% so you can see all the detail...
1. Make sure that you have the Belt routed exactly through the same path as is on the picture.
2. Make sure there is no obstruction keeping the idler arm from moving and taking up the slack in the belt (grass, sticks, dirt, etc get into the way sometimes keeping the spring from being able to pull it as far as it needs to move.
3. Make sure the sping is in good condition and is hooked to the right places to be able to maximize tension. (with out a good spring hooked the right place, you will not have enough tension and too much slack on the belt).
4. See if there is any way to adjust tension on the spring (I do not think there is, but put this in just in case there was a modification on your serial number that the photos don't show).
5. Examine the conditon of the Idler Pulley to make sure it spins very freely and does not wobble or have sharp edges. I woudl hate for you to have to replace a new belt because of a pulley cutting it or being worn.
6. If this does not solve the problem, the answer is to replace the deck belt.
REASON... These belts are in the shape of a V riding in pullyey that are also V shaped.
The belt rides on its SIDES in these pulleys making contact with the IN-sides of the pulley.
As the belt wears, it gets THINNER on the sides.
It therefore goes deeper into the V grove of each of the pulley's and in effect makes the Pulley seem Smaller in diameter. This effectively makes the PATH that the belt travels actually Shorter because it does not have to travel as far around each pulley (only an inch or two.
Ad to this that the belt does stretch a bit (only a tiny bit) and you have much to much slack.
So Often the answer to "How can I tighten the belt on a McCulloch Lawn Tractor" is
Replace the Belt...
Always see if you can replace the belt with the exact part number from the manufacturer. It will be the right length and be the right tension.
If you can not, make sure when they measure your belt, they adjust for the stretch and wear of your belt...